Method for the manufacture and recovery of methyl tertiary butyl ether

ABSTRACT

A method for the preparation of methyl tertiary butyl ether is provided wherein a mixture of methanol and substantially peroxides-free tertiary butyl alcohol are catalytically reacted to form a reaction product that is separated into a first lighter distillation fraction comprising isobutylene, methanol and methyl tertiary butyl ether and a second heavier distillation fraction comprising methanol, tertiary butyl alcohol and water, wherein the first distillation fraction and a first recycle isobutylene fraction are reacted to form an isobutylene conversion product that is charged, together with recycle isobutylene to a methanol extraction zone and countercurrently contacted with water to provide an overhead extract comprising aqueous isobutylene, and wherein the isobutylene is recovered and recycled.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

This invention relates to a method for the manufacture and purificationof methyl tertiary butyl ether. More particularly, this inventionrelates to a method for the manufacture of methyl tertiary butyl etherfrom tertiary butyl alcohol and methanol and for the purification of themethyl tertiary butyl ether formed by the reaction.

2. Prior Art

In U.S. Pat. No. 4,144,138 (1979) to Rao et al., there is disclosed amethod for recovering methyl tertiary butyl ather from etherificationreaction effluent by azeotropic distillation to recover methanol-etherazeotrope overhead which is water-washed to give pure ether raffinate,the latter being azeotropically distilled to yield ether-methanoloverhead which is recycled to water washing.

The preparation of methyl tert-butyl ether from methyl and tert-butylalcohols is discussed in S. V. Rozhkov et al., Prevrashch Uglevodorodov,Kislotno Osnovn. Geterogennykh Katal. Tezisy Dokl., Vses. Konf., 1977,150 (C. A. 92:58165y). Here the TBA and methanol undergo etherificationover KU-2 strongly acidic sulfopolystyrene cation-exchangers under mildconditions. This reference contains data on basic parameters of such aprocess.

3. Background Information

Methyl tert-butyl ether is finding increasing use as a blendingcomponent in high octane gasoline as the current gasoline additivesbased on lead and manganese are phased out. Currently all commercialprocesses for the manufacture of methyl tert-butyl ether are based uponthe liquid-phase reaction of isobutylene and methanol catalyzed by acationic ion-exchange resin.

With the expanding use of MTBE as an acceptable gasoline additive, agrowing problem is the availability of raw materials. Historically, thecritical raw material is isobutylene (Oil and Gas J., Jun. 8, 1987, p.55). It would be advantageous, therefore, to have a process to make MTBEthat does not require isobutylene as a building block. It would beadvantageous to have an efficient process for making MTBE by reaction ofmethanol with tertiary butyl alcohol, since t-butanol (TBA) is readilyavailable commercially through isobutane oxidation.

It is known to react methanol with tertiary butyl alcohol in thepresence of a catalyst in order to produce methyl tertiary butyl ether.A wide variety of catalysts have been suggested for this purpose.

In U.S. Pat. No. 2,282,469 to Frolich there is disclosed a process forpreparing methyl tertiary butyl ether over a catalyst comprisingKieselguhr impregnated with phosphoric acid at a temperature of about175° F. to 350° F.

Japanese Patent No. 0007432 teaches the use of zeolites to make dialkylethers containing primary or secondary alkyl groups. The zeolites have aporous structure and are represented by:

    M.sub.2/n O·Al.sub.2 O.sub.3 ·xSiO.sub.2 ·.sub.y H.sub.2 O

where M is an alkali metal or alkaline earth metal cation or organicbase cation, n is the valence of the cation and x and y are variables.

U.S. Pat. No. 4,058,576 to Chang et al. teaches the use of(pentasil-type) aluminosilicate zeolites, such as ZSM-5, having a poresize greater than 5 angstrom units and a silica-to-alumina ratio of atleast 12, to convert lower alcohols to a mixture of ethers and olefins.

In U.S. Pat. No. 4,822,921 there is disclosed a method for producingMTBE by reacting tertiary butyl alcohol and methanol in the presence ofa catalyst comprising an inert support, such as titania, having aphosphoric acid impregnated thereon.

U.S. Pat. No. 4,827,048 discloses a method for producing MTBE byreacting tertiary butyl alcohol and methanol in the presence of acatalyst comprising a heteropoly acid such as 12-tungstophosphoric acidor 12-molybdophosphoric acid on an inert support, such as titania.

Two of the principal by-products formed during the reaction of themethanol with the tertiary butyl alcohol are water and isobutylene.Methanol and methyl tertiary butyl ether form an azeotrope which isbroken only with difficulty and therefore the separation of methanolfrom MTBE during the recovery of purified methyl tertiary butyl etherpresents a serious problem.

In U.S. Pat. No. 4,820,877, separation of methanol from MTBE isaccomplished by using a refinery fuel gas to enhance the separation ofmethanol into the overhead stream of a distillation column.

In U.S. Pat. No. 4,814,517, separation of methanol from MTBE isaccomplished by using a silica gel to preferentially adsorb methanolfrom an MTBE stream and by periodically regenerating the silica gel.

In U.S. Pat. No. 4,798,674, separation of methanol from MTBE isaccomplished by using a membrane of cross-linked polyvinyl alcohol or aquaternary ammonium ion resin. Methanol preferentially permeates throughthe membrane increasing the MTBE concentration of the charge liquid.

In U.S. Pat. No. 4,759,850, separation of methanol from MTBE isaccomplished by reverse osmosis.

In U.S. Pat. No. 4,440,963, separation of methanol from MTBE isaccomplished by adding an agent such as 2-methyl pentane or Freon 113 toform an azeotrope with methanol. This azeotrope is recovered overheadgiving a methanol-free MTBE bottoms product.

As recognized by Rao et al. in U.S. Pat. No. 4,144,138, isobutylene isformed as a by-product when methanol is reacted with tertiary butylalcohol. In accordance with the Rao process, the isobutane is separatedfrom the reaction product in an initial azeotropic distillation step asa noncondensable gas. Rao teach that the part of the isobutane may beflashed from the reaction product for recycle, depending upon purity.

SUMMARY OF THE INVENTION

It has been discovered that isobutylene is formed when methanol isreacted with tertiary butyl alcohol in an etherification reaction zoneto form methyl tertiary butyl ether, the primary product.

In accordance with the present invention, a process is provided whereinisobutylene is utilized downstream of the etherification reaction zoneas an extractant in the purification of the methyl tertiary butyl ether,and as a reactant, together with methanol, in the preparation ofadditional methyl tertiary butyl ether.

Also, when tertiary butyl alcohol is prepared from tertiary butylhydroperoxide the tertiary butyl alcohol reaction product will containminor amounts of peroxide contaminants such as tertiary butylhydroperoxide, ditertiary butyl peroxide, allyl tertiary butyl peroxide,etc. When tertiary butyl alcohol contaminated with minor amounts ofperoxides is reacted with methanol to form methyl tertiary butyl ether,the etherification reaction product resulting from the reaction willcontain the peroxide contaminants.

In accordance with another embodiment of the present invention, aperoxides-contaminated tertiary butyl alcohol feedstock is passedthrough a peroxides decomposition reaction zone before being charged tothe methyl tertiary butyl ether etherification reaction zone so that themethyl tertiary butyl ether etherification product will be substantiallyfree from peroxide contaminants.

In accordance with a further embodiment of the present invention, anintegrated process is provided wherein a peroxides-contaminated tertiarybutyl alcohol feedstock is passed through a peroxides decompositionreaction zone to substantially completely decompose the peroxidecontaminants contained therein, and then charged to a methyl tertiarybutyl ether etherification reaction zone together with methanol to forman isobutylene-containing methyl tertiary butyl ether etherificationproduct that is substantially free from peroxide contaminants, whereinby-product isobutylene is utilized downstream of the etherificationreaction zone as an extractant in the purification of the methyltertiary butyl ether and wherein the by-product isobutylene is used as areactant in the preparation of additional methyl tertiary butyl ether.

DESCRIPTION OF PREFERRED EMBODIMENTS I

In accordance with a preferred embodiment of the present invention, amethod for the continuous preparation of methyl tertiary butyl ether(MTBE) from tertiary butyl alcohol (TBA) and methanol (MeOH) is providedcomprising the steps of:

a) continuously charging a peroxides-contaminated tertiary butyl alcoholfeedstock to a peroxides decomposition reaction zone and substantiallycompletely decomposing the peroxide contaminants therein to form asubstantially peroxides-free tertiary butyl alcohol product,

b) continuously charging a reaction feed mixture comprising methanol andthe substantially peroxides-free tertiary butyl alcohol product to anetherification reaction zone containing a bed of a TBA/MeOHetherification catalyst and reacting said reaction feed mixture thereinto form an etherification reaction product comprising unreactedmethanol, unreacted tertiary butyl alcohol, water, isobutylene andmethyl tertiary butyl ether,

c) continuously charging the etherification reaction product to a firstmethyl tertiary butyl ether distillation zone and separating it thereininto a first lighter distillation fraction comprising isobutylene,methanol and methyl tertiary butyl ether and a second heavierdistillation fraction comprising methanol, tertiary butyl alcohol andwater,

d) continuously charging an isobutylene reaction mixture comprising thefirst distillation fraction and a first recycle isobutylene (IBTE)fraction to an isobutylene conversion reaction zone containing a solidresin IBTE/MeOH etherification catalyst and partially reacting theisobutylene and methanol contained in the isobutylene reaction mixtureto form an isobutylene conversion product,

e) continuously charging an extraction feed mixture comprising theisobutylene conversion product and a second isobutylene recycle fractionto a methanol extraction zone and countercurrently contacting theextraction feed mixture therein with water to provide an overheadextract comprising isobutylene, methyl tertiary butyl ether and a minoramount of water, and a raffinate comprising methanol, water and a minoramount of methyl tertiary butyl ether,

f) continuously charging the extract to a second methyl tertiary butylether distillation zone and separating it therein into a third lighterdistillation fraction comprising isobutylene and water and a fourthheavier distillation fraction consisting essentially of methyl tertiarybutyl ether,

g) continuously charging the third distillation fraction to adecantation separation zone and separating it therein into anisobutylene fraction and a water fraction,

h) continuously recycling a first portion of said isobutylene fractionto the isobutylene reaction conversion zone as the first isobutylenerecycle fraction, and

i) continuously recycling a second portion of said isobutylene fractionto the methanol extraction zone as the second isobutylene recyclefraction.

II

Another preferred embodiment of the present invention comprises a methodfor the continuous preparation of methyl tertiary butyl ether fromtertiary butyl alcohol (TBA) and methanol (MeOH), including:

b') continuously reacting a mixture of methanol and tertiary butylalcohol in an etherification reaction zone containing a bed of aTBA/MeOH etherification catalyst to form an etherification reactionproduct comprising unreacted methanol, unreacted tertiary butyl alcohol,water, isobutylene and methyl tertiary butyl ether,

c') continuously charging the etherification reaction product to a firstmethyl tertiary butyl ether distillation zone and separating it thereininto a first lighter distillation fraction comprising isobutylene,methanol and methyl tertiary butyl ether and a second heavierdistillation fraction comprising methanol, tertiary butyl alcohol andwater,

d') continuously charging an isobutylene reaction mixture comprising thefirst distillation fraction and a first recycle isobutylene (IBTE)fraction to an isobutylene conversion reaction zone containing a solidresin IBTE/MeOH etherification catalyst and partially reacting theisobutylene and methanol contained in the isobutylene reaction mixtureto form an isobutylene conversion product,

e') continuously charging an extraction feed mixture comprising theisobutylene conversion product and a second isobutylene recycle fractionto a methanol extraction zone and countercurrently contacting theextraction feed mixture therein with water to provide an overheadextract comprising isobutylene, methyl tertiary butyl ether and a minoramount of water, and a raffinate comprising methanol, water and a minoramount of methyl tertiary butyl ether,

f') continuously charging the extract to a second methyl tertiary butylether distillation zone and separating it therein into a third lighterdistillation fraction comprising isobutylene and water and a fourthheavier distillation fraction consisting essentially of methyl tertiarybutyl ether,

g') continuously charging the third distillation fraction to adecantation separation zone and separating it therein into anisobutylene fraction and a water fraction,

h') continuously recycling a first portion of the isobutylene fractionto the isobutylene reaction zone as the first isobutylene recyclefraction, and

i') continuously recycling a second portion of said isobutylene fractionto the methanol extraction zone as the second isobutylene recyclefraction.

III

In accordance with a third preferred embodiment of the presentinvention, a method for the continuous preparation of methyl tertiarybutyl ether is provided wherein the second heavier distillation fractionfrom the first methyl tertiary butyl ether distillation zone and theraffinate from the methanol extraction zone are further processed inorder to recover the methyl tertiary butyl ether contained therein andin order to obtain the methanol and tertiary butyl alcohol containedtherein for recycle, comprising the steps of:

j) continuously charging the raffinate from the methanol extraction zoneto a third methyl tertiary butyl ether distillation zone and separatingit therein into a lighter fifth distillation fraction comprising methyltertiary butyl ether and a heavier sixth distillation fractioncomprising water and methanol,

k) continuously charging the sixth distillation fraction to a fourthmethanol distillation zone and separating it therein into a seventhlighter methanol recycle fraction and an eighth heavier distillationfraction,

l) continuously charging the second heavier distillation fraction to afifth distillation zone and separating it therein into a ninth lighterdistillation recycle fraction comprising methanol and tertiary butylalcohol, and a tenth heavier distillation fraction,

m) continuously charging the fifth distillation fraction to the methanolextraction zone, and

n) continuously charging the seventh distillation fraction and the ninthdistillation fractions to the etherification reaction zone.

DETAILED DESCRIPTION OF THE PRESENT INVENTION The EtherificationReaction Catalyst

In accordance with the MTBE manufacture and purification method of thepresent invention, an etherification reaction zone containing a bed ofetherification catalyst is utilized. A wide variety of etherificationcatalysts can be used for this purpose, such as supported phosphorusacid-type catalysts. A preferred catalyst is a sulfonic acid resinetherification catalyst such as a sulfonated polystyrene resincross-linked with divinyl benzene.

Any suitable solid resin etherification catalyst may be used for thispurpose, such as a strongly acidic ion exchange resin consistingessentially of sulfonated polystyrene, such as a divinyl benzenecrosslink polystyrene matrix containing from about 0.5 to about 20% ofcopolymerized divinyl benzene. Resins of this nature are manufacturedand sold commercially under various trade names such as "Dowex 50","Nalcite HCR" and "Amberlyst 15". The use of catalyst of this nature isdisclosed, for example, in Rao U.S. Pat. No. 4,144,138.

Also, Kieselguhr impregnated with phosphoric acid as disclosed inFrolich U.S. Pat. No. 2,282,469, titania having phosphoric acidimpregnated thereon as disclosed in Knifton U.S. Pat. No. 4,822,921, ahetero polyacid such as 12-tungstophosphoric acid or12-molybdophosphoric acid supported on titania, etc., may be used.

Zeolites as disclosed in Japanese Patent No. 0007432 or aluminosilicatezeolites as disclosed in Chang et al. U.S. Pat. No. 4,058,576 may alsobe used.

The reaction conditions to be utilized when reacting methanol withtertiary butyl alcohol in the presence of a sulfonic acid resinetherification catalyst of the type disclosed in the prior art include areaction temperature of about 90° to about 140° C., a pressure of about30 to about 500 psia and a space velocity of about 0.5 to about 20volumes of feed per volume of etherification catalyst per hour.

The Solid Resin Etherification Catalyst

In accordance with the present invention, a distillate fraction obtainedduring the recovery process, identified above as the first distillationfraction, and which contains both isobutylene and methanol is broughtinto contact with a solid resin etherification catalyst, as describedabove, in order to convert a significant portion of the isobutylene andmethanol to methyl tertiary butyl ether.

The first distillation fraction will normally contain from about 5 toabout 10 wt. % of isobutylene, from about 70 to about 80 wt. % of methyltertiary butyl ether and from about 10 to about 20 wt. % of methanol.

An isobutylene reaction mixture is prepared from the first distillationfraction and a first isobutylene recycle fraction so as to provide anisobutylene reaction mixture containing about an additional 1 to 10 wt.% of isobutylene, based on the weight of the first distillationfraction. Thus, the isobutylene reaction mixture may comprise from about6 to about 15 wt. % of isobutylene, from about 65 to about 75 wt. % ofmethyl tertiary butyl ether and from about 10 to about 20 wt. % ofmethanol.

Any suitable solid resin etherification catalyst may be used for thispurpose, such as a strongly acidic ion exchange resin consistingessentially of sulfonated polystyrene, such as a divinyl benzenecrosslink polystyrene matrix containing from about 0.5 to about 20% ofcopolymerized divinyl benzene. Resins of this nature are manufacturedand sold commercially under various trade names such as "Dowex 50","Nalcite HCR" and "Amberlyst 15". The use of catalyst of this nature isdisclosed, for example, in Rao U.S. Pat. No. 4,144,138.

The first distillation fraction will normally contain from about 5 toabout 10 wt. % of isobutylene, from about 70 to about 80 wt. % of methyltertiary butyl ether and from about 10 to about 20 wt. % of methanol.

It is contacted with a solid resin etherification catalyst in theisobutylene conversion reaction zone under conversion conditionsincluding, for example, a temperature of about 35° to about 130° C., apressure of about 30 to about 500 psia and a contact time of about 0.5to about 20 volumes of first distillate fraction per volume ofetherification catalyst per hour. As a consequence, an isobutyleneconversion product is formed which will normally contain from about 0 toabout 10 wt. % of isobutylene, about 75 to about 85 wt. % of methyltertiary butyl ether and from about 10 to about 15 wt. % of methanol.

Peroxide Decomposition

When the tertiary butyl alcohol feedstock to be used in the preparationof methyl tertiary butyl ether is tertiary butyl alcohol contaminatedwith peroxides such as tertiary butyl hydroperoxide, ditertiary butylperoxide, allyl tertiary butyl peroxide, etc., the feedstock is treatedfor the substantially complete removal of the peroxide contaminantsbefore it is charged to the methyl tertiary butyl ether etherificationzone.

It is known to prepare tertiary butyl alcohol by the thermal orcatalytic decomposition of tertiary butyl hydroperoxide. It is alsoknown to prepare tertiary butyl alcohol by the catalytic reaction oftertiary butyl hydroperoxide with propylene to form propylene oxide andtertiary butyl alcohol. The tertiary butyl alcohol feedstock derivedfrom tertiary butyl hydroperoxide in this manner will contain peroxidecontaminants. A typical feedstock prepared in this fashion will containfrom about 95 to 99 wt. % of tertiary butyl alcohol and less than about2.0 wt. % of peroxide contaminants.

In accordance with the present invention, the peroxides-contaminatedtertiary butyl alcohol is charged to a peroxides decomposition reactionzone where the peroxides are substantially completely thermally and/orcatalytically decomposed. The peroxide contaminants will be decomposedto form water and tertiary butyl alcohol, and trace amounts of otherdecomposition products such as acetone and methyl formate.

When the peroxides are to be thermally decomposed, theperoxides-contaminated tertiary butyl alcohol feedstock is continuouslypassed through a reactor in the peroxides decomposition reaction zonedat a temperature of about 100° to about 200° C., a pressure of about 80to about 500 psia at a flow rate of about 0.5 to 20 volumes of feedstockper reactor volume per hour to thereby provide a substantiallyperoxides-free tertiary butyl alcohol reaction product.

Alternately, the peroxide contaminants may be catalytically decomposed.

A wide variety of catalysts may be used for this purpose, such as cobaltborate as disclosed in U.S. Pat. No. 4,547,598, a nickel, copper,chromia catalyst as disclosed in Sanderson et al. U.S. Pat. No.4,704,482, an iron, copper, chromia, cobalt catalyst as disclosed inSanderson et al. U.S. Pat. No. 4,705,903, a base treated hydrogenationcatalyst from groups VIB or VIIIB of the Periodic Table as disclosed inSanderson et al. U.S. Pat. No. 4,742,179, a nickel, copper, chromium andbarium catalyst as disclosed in Sanderson et al. U.S. Pat. No.4,873,380, a metal phthalocyanine catalyst as disclosed in Sanderson etal. U.S. Pat. No. 4,910,349, an imidazole-promoted methyl metalphthalocyanine catalyst as disclosed in Sanderson et al. U.S. Pat. No.4,912,266, a base promoted metal phthalocyanine catalyst as disclosed inSanderson et al. U.S. Pat. No. 4,912,267, a solid ruthenium catalyst asdisclosed in Sanderson et al. U.S. Pat. No. 4,922,033, a promoted metalporphine catalyst as disclosed in Sanderson et al. U.S. Pat. No.4,922,034, etc.

The conversion conditions to be utilized in the peroxide decompositionzone may comprise, for example, a temperature of about 100° to about200° C., a pressure of about 80 to about 500 psia and a space velocityof about 0.5 to about 20 volumes of feed per volume of catalyst perhour.

The effluent from the peroxide decomposition zone will typicallycomprise about 95 to about 99 wt. % of tertiary butyl alcohol and lessthan about 0.1 wt % of peroxide contaminants.

BRIEF DESCRIPTION OF THE DRAWING

The drawing is a schematic flow sheet which conventional parts omittedshowing the general reaction and recovery sequence of the presentinvention for the manufacture and purification of methyl tertiary butylether.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Turning now to the drawing, there is shown a schematic flow sheetillustrating the preferred method for the practice of the process of thepresent invention. In the drawing, conventional parts, such as valves,pumps, temperature control sensors, pressure sensors, heaters, coolers,flow control regulation apparatus, reflux condenses, reboilers, etc.,have been omitted.

In accordance with the present invention, there is provided anetherification reaction zone 10 containing a bed of solid etherificationcatalyst. Any suitably etherification catalyst may be used such as, forexample, a solid resin etherification of the type described above, suchas a strongly acidic ion exchange resin consisting essentially ofsulfonated polystyrene crosslinked with divinyl benzene (e.g., Dowex 50,Nalcite HCR, Amberlyst 15, etc.). As another example, the catalyst maybe a fluorophosphoric acid-on-titania catalyst of the type disclosed inKnifton et al. U.S. Pat. No. 4,822,921 or a heteropoly acid such as12-tungstophosphoric acid or 12-molybdophosphoric acid supported on aninert support such as titania.

When the tertiary butyl alcohol is prepared by the thermal or catalyticdecomposition of tertiary butyl hydroperoxide, it will contain minoramounts of impurities such that, for example, the feedstock charged tothe reaction 10 will contain the following components:

    ______________________________________                                        ETHERIFICATION REACTION ZONE FEED MIXTURE                                                    wt. %                                                          Component      (approximate)                                                  ______________________________________                                        Methanol       41.0                                                           TBA.sup.1      47.0                                                           Acetone        0.5                                                            2-Propanol     6.0                                                            MTBE.sup.2     0.2                                                            DTBP.sup.3     0.1                                                            t-Butyl Formate                                                                              0.1                                                            Water          6.0                                                            ______________________________________                                         .sup.1 Tertiary butyl alcohol                                                 .sup.2 Methyl tertiary butyl ether                                            .sup.3 ditertiary butyl peroxide                                         

When the tertiary butyl alcohol feedstock to be initially charged toetherification reaction zone 10 is a peroxides-contaminated tertiarybutyl alcohol feedstock, as described above, the tertiary butyl alcoholfeedstock is initially peroxides decomposition zone 11, such as, forexample a thermal peroxides decomposition zone 11 operated, (e.g.) at atemperature of about 100° to about 200° C., a pressure of about 80 toabout 500 psia and a flow rate of about 0.5 to 20 volumes of feedstockper reactor volume per hour to thereby provide a substantiallyperoxides-free tertiary butyl alcohol reaction product. The peroxidecontaminants will be decomposed amounts of other decomposition productssuch as acetone and methyl formate.

The substantially peroxides-free tertiary butyl alcohol reaction productis continuously discharged from the peroxides decomposition zone 11 by adischarge line 17 leading to a manifold 12. Fresh methanol iscontinuously charged to the manifold 12 by a line 15, as is a recyclestream 112 containing recycle methanol and recycle tertiary butylalcohol. The flow of methanol and tertiary butyl alcohol to the manifold12 through the lines 15, 17 and 112 is regulated so that a molar excessof methanol is present in the line 14 leading to the etherificationreaction zone 10, such as, for example, a molar ratio of about 1.1 toabout 3 moles of methanol per mol of tertiary butyl alcohol.

Within the etherification reaction zone 10, the feed mixture is broughtinto contact with the bed of etherification catalyst, such as a sulfonicacid resin etherification catalyst under reaction conditions including apressure of about 30 to about 500 psia, and more preferably from about200 to about 300 psia, a temperature of about 30° to about 200° C., andmore preferably from about 80° to about 140° C., and still morepreferably from about 90° to about 130° C. When the catalyst is asupported phosphorus acid-type catalyst, the reaction temperature maysuitably be in the range of about 150° to about 190° C.

Contact time within the etherification reaction zone is suitably suchthat about 0.5 to about 20 volumes of feed mixture per volume ofetherification catalyst per hour are fed to the etherification reactionzone 10 and, more preferably from about 1 to about 4 volumes of feedmixture per volume of etherification catalyst per hour.

Within the etherification reaction zone 10, methanol will exothermicallyreact with the tertiary butyl alcohol to form methyl tertiary butylether which will be contained in a reaction product discharged from theetherification reaction zone 10 by way of a line 20 leading to a firstmethyl tertiary butyl ether (MTBE) distillation zone 30.

As a specific example, when the solid etherification catalyst is asulfonic acid resin such as Amberlyst 15 and when the molar ratio ofmethanol to tertiary butyl alcohol in the feed mixture charged to theetherification reaction zone 10 by the line 14 is within the ratio ofabout 2.0 moles of methanol per mole of tertiary butyl alcohol, and thereaction is conducted at a temperature of about 100° C. at a feed rateof about 2.0 volumes of feed mixture per volume of catalyst per hour,the etherification reaction product may have the composition in partshown by the following table:

    ______________________________________                                        ETHERIFICATION REACTION PRODUCT                                                      Component                                                                             %                                                              ______________________________________                                               Water   14.0                                                                  Methanol                                                                              27.6                                                                  Isobutylene                                                                           3.0                                                                   TBA.sup.1                                                                             14.1                                                                  MTBE.sup.2                                                                            34.5                                                                  Other.sup.3                                                                           6.8                                                            ______________________________________                                         .sup.1 Tertiary butyl alcohol                                                 .sup.2 Methyl tertiary butyl ether                                            .sup.3 Includes the acetone, propanol, ditertiary butyl peroxide, tertiar     butyl formate, etc. initially present in the tertiary butyl alcohol           feedstock.                                                               

The etherification reaction product charged to the first MTBEdistillation zone 30 by way the charge line 20 is fractionated thereinunder distillation conditions including a liquid reflux temperature ofabout 30° to about 100° C., and more preferably about 40° to about 80°C., a reboiler temperature of about 80° to about 115° C., and morepreferably from about 95° to about 105° C., and a pressure of about 15to about 60 psia, the distillation condition being selected such thatsubstantially all of the MTBE in the etherification reaction product 20is taken overhead from the first distillation zone 30 by a line 32. As aconsequence, the first distillation fraction 32 taken overhead from thedistillation zone 30 will comprise substantially all of the isobutyleneand substantially all of the methyl tertiary butyl ether and some of themethanol charged to the first distillation zone 30. The second heavierdistillation fraction 34 discharged from the first MTBE distillationzone 30 will comprise methanol, tertiary butyl alcohol and water.

In accordance with the present invention, the first distillationfraction 32 in admixture with recycle isobutylene added by a recycleline 89 is charged by way of manifold 33 and charge line 35 to anisobutylene conversion zone 40 containing a bed of solid resinetherification catalyst such as a bed of Amberlyst 15 sulfonatedpolystyrene-divinyl benzene copolymer acidic ion exchange resin.Suitably, the admixture in the line 35 will contain about 2 to about 15parts of recycle isobutylene per 100 parts of first distillationfraction 32.

Etherification reaction conditions established in the isobutyleneconversion zone 40 include, for example, a temperature of about 35° toabout 130° C., and more preferably from about 40° to about 70° C., apressure of about 50 to about 500 psia, and more preferably from about150 to about 250 psia, and a contact time of about 0.5 to about 4volumes of first distillation fraction per volume of solid resinetherification catalyst per hour. As a consequence, a portion of themethanol and isobutylene contained in the first distillation fraction 32will be converted to methyl tertiary butyl ether. Typically, theconversion will amount to about 30 to about 60 wt. %, based on theisobutylene.

As a consequence, there will be formed an isobutylene conversion productdischarged in the isobutylene conversion zone 40 by a line 42 leading toa methanol solvent extraction zone 50. The composition of a typicalisobutylene conversion product may be characterized as follows:

    ______________________________________                                        ISOBUTYLENE CONVERSION PRODUCT                                                       Component                                                                             wt. %                                                          ______________________________________                                               Isobutylene                                                                           5.4                                                                   MTBE    79.5                                                                  Methanol                                                                              12.2                                                                  Other   2.9                                                            ______________________________________                                    

In accordance with the present invention, the isobutylene conversionproduct 42 together with recycle isobutylene charged by a recycle line83 is charged to a manifold 44 and thence via line 46 to a methanolsolvent extraction zone 50 where it is countercurrently contacted withwater introduced into the solvent extraction zone 50 by a charge line 52controlled by a valve 54.

Within the methanol solvent extraction zone 50, solvent extractionconditions are established for countercurrent solvent extractionincluding a ratio of water to extraction feed mixture within the rangeof about 0.1 to about 0.3 parts of water per part of extraction feedmixture per hour, and more preferably a ratio of about 0.1 to about 0.2parts of water per part of extraction feed mixture. Extractiveconditions to be established may suitably include a temperature of about20° to about 60° C., and more preferably from about 30° to about 40° C.,and a pressure of about 50 to about 500 psia, and more preferably fromabout 50 to about 150 psia.

As a consequence, a supernatant extract will be formed which iswithdrawn from the methanol solvent extraction zone 50 by line 60. Theraffinate is discharged from the solvent extraction zone 50 by way of abottoms charge line 64 leading to a third methyl tertiary butyl etherdistillation zone 70.

Within the second methyl tertiary butyl ether purification distillationzone 62, distillation conditions are established including a liquidreflux temperature of about 30° to about 60° C., and more preferablyfrom about 40° to about 55° C., a reboiler temperature of about 100° toabout 140° C., and more preferably from about 125° to about 135° C. anda pressure of about 70 to about 120 psia, and more preferably from about90 to about 110 psia, to thereby form a lighter distillation fraction 66discharged from the second distillation zone 62 and a heavier fourthdistillation fraction 68 consisting essentially of product, namelymethyl tertiary butyl ether.

The third distillation fraction 66 will comprise a mixture ofisobutylene and water and suitably charged to a decantation zone 80where it can settle to form a supernatant isobutylene phase withdrawnfrom the decantation zone 80 by way of a line 82. Water is discharged inthe decantation zone 80 by way of a water discharge line 84 and issuitably purged from the system. A portion of the isobutylene in theline 82 is recycled by way of manifold 86, line 89 controlled by valve87, manifold 33 and line 35 to the isobutylene conversion reaction zone40 as a first isobutylene recycle fraction and another portion of theisobutylene in the line 82 is recycled to the methanol solventextraction zone 50 through a branch line 83 controlled by a valve 85 asa second isobutylene recycle fraction. Suitably, about 10 to about 15wt. % of the isobutylene in line 82 is discharged from manifold 86 asthe first isobutylene recycle fraction and about 90 to about 85 wt. % isdischarged as the second isobutylene recycle fraction.

The raffinate 64 charged to the third distillation zone 70 will comprisemethyl tertiary butyl ether, methanol and water, and is suitablyfractionated therein under distillation conditions including a liquidreflux temperature of about 30° to about 90° C., and more preferablyfrom about 50° to about 75° C., and a reboiler temperature of about 80°to about 120° C., and more preferably from about 105° to about 115° C.,and a pressure of about 15 to about 60 psia, and more preferably fromabout 40 to about 50 psia, to form a fifth lighter distillation fraction72 comprising methyl tertiary butyl ether which may suitably be chargedto the manifold 44 for the charge line 46 to the methanol solventextraction zone 50. A sixth heavier distillation fraction comprisingwater and methanol is discharged from the third distillation zone 70 bya line 74 leading to a fourth distillation zone 90. The sixthdistillation fraction charged to the fourth methanol distillation zone90 is fractionated therein under distillation conditions which maysuitably include a liquid reflux temperature of about 30° to about 80°C., and more preferably from about 60° to about 75° C., a reboilertemperature of about 100° to about 140° C., and more preferably fromabout 110° to about 120° C., and a pressure of about 15 to about 60psia, and more preferably from about 20 to about 30 psia, into a seventhlighter distillation fraction 92 which may be suitably charged to amanifold 93 and from thence by line 112 to the manifold 12 for recycleto the etherification reaction zone 10 through feed line 14. A heavierdistillation fraction consisting essentially of water is discharged fromthe fourth methanol distillation zone by way of a line 94 and may bedischarged from the system through manifold 95 and water discharge line96.

The second distillation fraction 34 discharged from the first MTBEdistillation zone 30 in accordance with the present invention is chargedto a fifth tertiary butyl alcohol recovery distillation zone 100 whereit is fractionated under distillation conditions including a liquidreflux temperature of about 35° to about 170° C., and more preferablyabout 140° to about 150° C., and a reboiler temperature of about 100° toabout 190° C., more preferably about 170° to about 180° C., and at apressure of about 15 to about 190 psia, and more preferably about 110 toabout 160psia, into a ninth distillation fraction discharged from thefifth distillation zone 100 by a line 102 leading to manifold 103 and atenth heavier distillation fraction comprising a third water fractiondischarged from the distillation zone 100 by a line 106 leading by wayof manifold 95 to the water discharge line 96.

In accordance with one embodiment of the present invention, the ninthdistillation fraction 102 is charged to a manifold 103 provided with adischarge line 118 controlled by a valve 116 leading to the feedmanifold 12 so that the methanol can be directly charged to theetherification reaction zone 10 from manifold 12 through feed line 14. Asecond branch line 120 controlled by a valve 98 is provided which leadsfrom manifold 103 to the feed manifold 44 for the methanol extractionzone 50 so that all or a portion of the ninth distillation fraction 102may be recycled to the manifold 44.

EXAMPLES

The invention will be further illustrated by the following specificexample(s) which, given by way of illustration, and not as a limitationon the scope of this invention. Where parts are mentioned, they areparts by weight.

In accordance with a preferred embodiment of the present invention, atertiary butyl alcohol feedstock is continuously charged to peroxidedecomposition zone 11 by a line 13 where it is thermally treated underthermal di-tertiary butyl peroxide decomposition conditions including atemperature of about 100° to about 200° C., a pressure of about 80 toabout 500 psia and a flow rate of about 0.5 to 4 volumes of feedstockper reactor volume per hour to thereby provide a substantiallyperoxides-free tertiary butyl alcohol reaction product.

The peroxides-contaminated feedstock and the substantiallyperoxides-free reaction product discharged from the peroxidedecomposition zone 11 will typically have compositions as follows:

    ______________________________________                                        PEROXIDE DECOMPOSITION ZONE                                                   FEED AND PRODUCT                                                                              Feed     Product                                              Component       (wt. %)  (wt. %)                                              ______________________________________                                        DTBP.sup.1      0.87     0.02                                                 TBA.sup.2       97.2     97.4                                                 Water           0.1      0.02                                                 Other.sup.3     1.8      2.6                                                  ______________________________________                                         .sup.1 Ditertiary butyl peroxide                                              .sup.2 Tertiary butyl alcohol                                                 .sup.3 Includes acetone, tertiary butyl formate, isoporpyl alcohol, etc. 

The substantially peroxides-free tertiary butyl reaction product 17 ischarged to the manifold 12 together with fresh methanol feedstock 15 andthe recycle fraction 112 in amounts, for example, such that the chargeratio of methanol to tertiary butyl alcohol in the feed line 14 amountsto about 2 moles of methanol per mole of tertiary butyl alcohol.

The feed mixture is discharged from the manifold 12 by a line 14 leadingto etherification reaction zone reactor 10 containing a bed of asuitable etherification catalyst, such as Amberlyst 15 catalyst. Withinthe etherification reaction zone, the feedstock is passed through theetherification reaction bed on a continuous basis under reactionconditions, as described above, to thereby provide a reaction producthaving the following composition:

    ______________________________________                                        ETHERIFICATION REACTION ZONE                                                  REACTION PRODUCT                                                                             wt. %                                                                 Component                                                                             (approx.)                                                      ______________________________________                                               Methanol                                                                              2.8                                                                   TBA     14.5                                                                  Water   14.0                                                                  Isobutylene                                                                           3.0                                                                   MTBE    34.5                                                                  Acetone 0.4                                                                   2-Propanol                                                                            6.0                                                            ______________________________________                                    

The etherification zone reaction product is discharged from the reactionzone 10 by a line 20 leading to first methyl tertiary butyl etherdistillation zone 30 where the fraction 20 is separated into firstlighter distillation fraction 32 comprising about 6.5 wt. % isobutylene,about 16.5 wt. % methanol and about 75 wt. % MTBE and a second heavierfraction comprising about 37 wt. % methanol, about 26.0 wt. % tertiarybutyl alcohol, about 26 wt. % water, 11 wt. % isopropanol and about 0.5wt. % of other components.

The first distillation fraction 32 along with recycle isobutylene 89 iscontinuously charged to an isobutylene conversion zone 40 through theline 34 and brought into contact therein with a solid resinetherification catalyst, such as Amberlyst 15 catalyst, under conversionconditions, as described above, to thereby convert about 50 wt. % of theisobutylene and a portion of the methanol in the first distillationfraction to MTBE and to form an isobutylene conversion product which isdischarged from the isobutylene reaction zone 40 by a line 42 and whichtypically has the following composition:

    ______________________________________                                        ISOBUTYLENE CONVERSION FEED AND                                               PRODUCT, wt. %                                                                Component        Feed   Product                                               ______________________________________                                        Isobutylene      11     5.5                                                   MTBE             71     80                                                    Methanol         15     12                                                    Other             3     3                                                     ______________________________________                                    

The isobutylene conversion fraction 42 and the isobutylene recyclefraction 83 are continuously charged to the manifold 44 by a line 41leading from manifold 45. The isobutylene mixture is discharged from themanifold 44 together with recycle fraction 120 and recycle fraction 72by a feed line 46 leading to methanol extraction zone 50 in the ratio ofabout 2 parts of isobutylene conversion product per part of recycleisobutylene. Water is charged to the methanol extraction zone 50 by awater charge line 52 in an amount such that the ratio of water toisobutylene and isobutylene conversion product in the methanolextraction zone 50 is in the range of about 0.1 to about 0.3 parts ofwater per part of etraction feed mixture.

Within the methanol extraction zone, the methanol is extracted from theisobutylene conversion product under extraction conditions as describedabove to thereby provide an overhead (extract) fraction 60 comprisingisobutylene and methyl tertiary butyl ether and a raffinate 64comprising methanol and water.

The extract is fed by a line 60 to a second methyl tertiary butyl etherpurification distillation zone 62 where it is resolved by distillationinto a third lighter distillation fraction 66 comprising isobutylene andwater and into a fourth heavier distillation fraction 68 consistingessentially of methyl tertiary butyl ether which is discharged asproduct.

The third distillation fraction 66 is charged to a decantationseparation zone 80 where it is permitted to settle and is resolved intoan isobutylene fraction 82 and a first water fraction 84 which isdischarged from the system.

The isobutylene fraction 82 is suitably recycled to the isobutyleneconversion zone 40 in admixture with the first distillation fraction 32and to the feed to the methanol extraction zone.

Typically, about 2 to about 10 parts of recycle isobutylene from theline 89 will be mixed with 100 parts of overhead product from the firstdistillation fraction 32.

The raffinate 64 is continuously charged to a third methyl tertiarybutyl ether distillation zone 70 where it is separated into a lighterfifth distillation fraction 72 comprising methyl tertiary butyl etherand a sixth heavier distillation fraction 74 comprising methanol andwater. The fraction 74 is continuously charged to a fourth methanoldistillation zone 90 wherein it is separated by fractional distillationinto a seventh lighter distillation fraction 92 comprising methanol andan eighth distillation fraction comprising water which is discharged bya line 94. In accordance with the preferred embodiment of the presentinvention, the fraction 92 together with fraction 118 is charged by aline 112 to feed manifold 12.

The second distillation fraction 34 from the first MTBE distillationzone 30 is continuously charged to a fifth tertiary butyl alcoholrecovery distillation zone 100 where it is separated into a ninthlighter distillation fraction 102 comprising methanol, tertiary butylalcohol and water and a tenth heavier distillation fraction 106comprising water. The tenth heavier distillation fraction is dischargedby a line 106 and the water in line 106, together with the water in line94, may suitably discharge from the system from manifold 95 throughwater discharge line 96.

Having thus described our invention, what is claimed is:
 1. A method forthe continuous preparation of methyl tertiary butyl ether (MTBE) fromtertiary butyl alcohol (TBA) and methanol (MeOH), which comprises thesteps of:a) continuously charging a peroxides-contaminated tertiarybutyl alcohol feedstock to a peroxides decomposition reaction zone andsubstantially completely decomposing the peroxide contaminants thereinto form a substantially peroxides-free tertiary butyl alcohol product;b) continuously passing a feed mixture comprising said substantiallyperoxides-free tertiary butyl alcohol product and methanol through amethyl tertiary butyl ether etherification reaction zone containing abed of a TBA/MeOH etherification catalyst under etherification reactionconditions to form an etherification reaction product comprisingunreacted methanol, unreacted tertiary butyl alcohol, water, isobutylene(IBTE) and methyl tertiary butyl ether; c) continuously charging saidetherification reaction product to a first methyl tertiary butyl etherdistillation zone and separating it therein into a first lighterdistillation fraction comprising isobutylene, methanol and methyltertiary butyl ether and a second heavier distillation fractioncomprising methanol, tertiary butyl alcohol and water; d) continuouslycharging an extraction feed mixture comprising said first lighterdistillation fraction and an isobutylene recycle fraction to a methanolextraction zone and countercurrently contacting the extraction feedmixture therein with water to provide an overhead extract comprisingisobutylene, methyl tertiary butyl ether and a minor amount of water anda raffinate comprising methanol, water and a minor amount of methyltertiary butyl ether; e) continuously charging the extract to a secondmethyl tertiary butyl ether distillation zone and separating it thereininto a third lighter distillation fraction comprising isobutylene andwater and a fourth heavier distillation fraction consisting essentiallyof methyl tertiary butyl ether; f) continuously charging the thirddistillation fraction to a decantation separation zone and separating ittherein into an isobutylene fraction and a water fraction; g)continuously recycling a portion of said isobutylene fraction to themethanol extraction zone as the isobutylene recycle fraction.
 2. Amethod as in claim 1 wherein the said peroxides decomposition reactionzone is a thermal peroxides decomposition reaction zone and whereinthermal peroxide decomposition reaction conditions are established insaid thermal peroxides decomposition reaction zone including atemperature of about 100° to 200° C., a pressure of about 80 to about500 psia and a flow rate of about 0.5 to 4 volumes of feedstock perreactor volume per hour.
 3. A method as in claim 1 wherein the methanoland tertiary butyl alcohol are charged to the methyl tertiary butylether etherification reaction zone in the molar ratio of about 1.1 toabout 3.0 moles of methanol per mole of tertiary butyl alcohol.
 4. Amethod as in claim 3 wherein the etherification catalysts in the methyltertiary butyl ether etherification zone is a solid resin divinylbenzene cross-linked sulfonated polystyrene catalyst.
 5. A method as inclaim 4 wherein the methanol is reacted with the tertiary butyl alcoholin the methyl tertiary butyl ether etherification zone under conversionconditions including a temperature of about 90° C. to about 140° C. anda pressure of about 30 to 500 psia at a flow rate of about 0.5 to 20volumes of feed mixture per volume of etherification catalyst per hour.6. A method as in claim 5 including the additional steps of:continuouslycharging an isobutylene reaction mixture comprising said firstdistillation fraction and another portion of said isobutylene fraction,as an isobutylene recycle fraction, to an isobutylene conversionreaction zone containing a solid resin IBTE/MeOH etherification catalystand partially reacting the isobutylene an methanol to form anisobutylene conversion product comprising isobutylene, methanol, methyltertiary butyl ether and water, and continuously charging saidisobutylene conversion product to said methanol extraction zone togetherwith said first lighter distillation fraction.
 7. A method as in claim 6wherein the isobutylene reaction mixture is reacted with isobutylene inthe isobutylene conversion reaction zone under reaction conditionsincluding a temperature of about 35° to about 130°, a pressure of about50 to 5000 psia and a flow rate of about 0.5 to about 4 volumes ofreaction mixture per volume of catalyst per hour, andwherein theextraction feed mixture is countercurrently contacted with water in themethanol extraction zone in the ratio of about 0.1 to about 0.3 parts ofwater per part of extraction feed mixture under extraction conditionsincluding a temperature of about 20° to about 60° C. and a pressure ofabout 50 to 5000 psia.
 8. A method as in claim 5 including theadditional steps of:j) continuously charging the raffinate from themethanol extraction zone to a third methyl tertiary butyl etherdistillation zone and separating it therein into a lighter fifthdistillation fraction comprising methyl tertiary butyl ether and aheavier sixth distillation fraction comprising water and methanol, k)continuously charging the sixth distillation fraction to a fourthmethanol distillation zone and separating it therein into a seventhlighter methanol recycle fraction and an eighth heavier distillationfraction, l) continuously charging the second heavier distillationfraction to a fifth distillation zone and separating it therein into alighter ninth distillation recycle fraction comprising methanol andtertiary butyl alcohol, and a heavier tenth distillation fraction, m)continuously charging the fifth distillation fraction to the methanolextraction zone, and n) continuously charging the seventh distillationfraction and the ninth distillation fractions to the methyl tertiarybutyl ether etherification reaction zone.
 9. A method for the continuouspreparation of methyl tertiary butyl ether (MTBE) from tertiary butylalcohol (TBA) and methanol (MeOH), which comprises the steps of:b')continuously reacting a feed mixture of methanol and tertiary butylalcohol in a methyl tertiary butyl ether etherification reaction zonecontaining a bed of a TBA/MeOH etherification catalyst to form anetherification reaction product comprising unreacted methanol, unreactedtertiary butyl alcohol, water, isobutylene and methyl tertiary butylether, c') continuously charging the etherification reaction product toa first methyl tertiary butyl ether distillation zone and separating ittherein into a first lighter distillation fraction comprisingisobutylene, methanol and methyl tertiary butyl ether and a secondheavier distillation fraction comprising methanol, tertiary butylalcohol and water, d') continuously charging an isobutylene reactionmixture comprising the first distillation fraction and a first recycleisobutylene (IBTE) fraction to an isobutylene conversion reaction zonecontaining a solid resin IBTE/MeOH etherification catalyst and partiallyreacting the isobutylene and methanol contained in the isobutylenereaction mixture to form an isobutylene conversion product, e')continuously charging an extraction feed mixture comprising theisobutylene conversion product and a second isobutylene recycle fractionto a methanol extraction zone and countercurrently contacting theextraction feed mixture therein with water to provide an overheadextract comprising isobutylene, methyl tertiary butyl ether and a minoramount of water, and a raffinate comprising methanol, water and a minoramount of methyl tertiary butyl ether, f') continuously charging theextract to a second methyl tertiary butyl ether distillation zone andseparating it therein into a third lighter distillation fractioncomprising isobutylene and water and a fourth heavier distillationfraction consisting essentially of methyl tertiary butyl ether, g')continuously charging the third distillation fraction to a decantationseparation zone and separating it therein into an isobutylene fractionand a water fraction, h') continuously recycling a first portion of theisobutylene fraction to the isobutylene reaction zone as the firstisobutylene recycle fraction, and i') continuously recycling a secondportion of said isobutylene fraction to the methanol extraction zone asthe second isobutylene recycle fraction.
 10. A method as in claim 9wherein the methanol and tertiary butyl alcohol are charged to themethyl tertiary butyl ether etherification reaction zone in the molarratio of about 1.1 to about 3.0 moles of methanol per mole of tertiarybutyl alcohol.
 11. A method as in claim 9 wherein the etherificationcatalysts in the methyl tertiary butyl ether etherification zone and inthe isobutylene conversion reaction zone are solid resin divinyl benzenecross-linked sulfonated polystyrene catalysts.
 12. A method as in claim9 wherein the methanol is reacted with the tertiary butyl alcohol in themethyl tertiary butyl ether etherification zone under conversionconditions including a temperature of about 90° to about 140° C. and apressure of about 30 to 500 psia at a flow rate of about 0.5 to 20volumes of feed mixture per volume of etherification catalyst perhour,wherein the isobutylene reaction mixture is reacted in theisobutylene conversion reaction zone under reaction conditions includinga temperature of about 35° to about 130° C., a pressure of about 50 to500 psia and a flow rate of about 0.5 to about 4 volumes of reactionmixture per volume of catalyst per hour, and wherein the extraction feedmixture is countercurrently contacted with water in the methanolextraction zone in the ratio of about 0.1 to about 0.3 parts of waterper part of extraction feed mixture under extraction conditionsincluding a temperature of about 20° to about 60° C. and a pressure ofabout 50 to 500 psia.